The prime objective of this proposed research is to define the role of specific brain stem loci in the integration of peripheral and central chemoreceptor afferent stimuli. A necessary prerequisite for this definition of brain stem function is a characterization of the action of peripheral chemoreceptors in ventilatory drive induced by conditions of simultaneous CO2 and O2 stimulation. Characterization of peripheral chemoreceptor function will be accomplished by a physiological isolation of stimulus presentation to the carotid body and central medullary chemoreceptor area of decerebrate cats. The effect of ablation of brain stem and nuclei and tract upon the set point and gain functions of the CO2 and O2 controller will be evaluated. Evidence obtained in the latter investigation will correlate the function of the brain stem sites with the integration of afferent chemoreceptor stimuli. Results of this proposed research will serve to draw together much anatomical and physiologcal information into an operational model of brain stem regulation of respiratory activity.